Machine tool probe

ABSTRACT

A probe has internal circuitry capable of operating in a plurality of different modes, for example a variety of filter modes and turn off modes. A switch on the probe sends an input to a controller which is arranged to set the mode in response to operation of the switch. The switch may be a push button which is operated externally of the probe by means of an actuator in the form of a plunger. The probe has a workpiece-contacting stylus mounted on a seat from which it is deflectable. The stylus and the seat may comprise the switch. An indicator, e.g., an LED, indicates the mode in response to an output from the controller. The controller outputs a plurality of indications of different modes in a sequence and a mode is selected by operating the switch once the desired mode is indicated.

This is a Continuation of application Ser. No. 10/362,572, filed Feb.24, 2003, which in turn is a National Stage Application ofPCT/GB02/00465, filed Feb. 1, 2002, which claimed priority from GB0102750.7, filed Feb. 2, 2001 and GB 0112998.0, filed May 30, 2001. Theentire disclosures of the prior applications are hereby incorporated byreference herein in their entirety.

BACKGROUND

This invention relates to probes for use on position determiningapparatus such as coordinate measuring machines, measuring robots and inparticular machine tools.

An example of such a probe is shown in U.S. Pat. No. 4,153,998. Probesintended for use on machine tools, in which there is a wireless signaltransmission system between the probe and the controller of the machinetool, are shown in European Patent Numbers 337669 and 337670.

As such probes have become more complex over the years, there has been aneed for them to operate in different modes.

For example, it can be desirable for the signal produced by the probe tobe filtered prior to transmitting it to the controller, in order toprevent the generation of spurious signals as a result of vibration.Therefore, the probe may be preset to use different types of filtering,or no filtering, depending on the machine tool and the environment intowhich it has been installed.

Furthermore, on machine tools such probes are commonly battery operated.The wireless signal transmission system also includes a receiver forreceiving a switch-on or start signal. This switches the probe on from asleeping state in which it consumes very low current, ready for normaluse. It is then desirable to switch the probe circuitry off (back to thesleeping state) after use. The probe may have different preset modes,giving different manners in which the circuitry is turned off.

In known probes, such modes are preset by the use of DIP switches on acircuit board internally within the probe. This has a number ofdisadvantages. In order to change the preset mode, the operator has todismantle the probe to access the DIP switches. There is a risk that theoperator will damage the printed circuit board, and the probe has to bedesigned to permit such dismantling. Where the DIP switches act on amicro controller to preset the mode, there is a restriction on thenumber of input lines to the micro controller.

With, say, three such input lines from a three-gang DIP switch, amaximum of eight modes can be preset. Any more modes would require alarger number of input lines to the micro controller. Finally, it wouldbe desirable to provide a pre-setting device which is smaller, lessexpensive and more reliable than DIP switches.

SUMMARY

The present invention provides a probe for position determiningapparatus, having internal circuitry capable of operating in a pluralityof different modes, a switch, a controller connected to receive an inputfrom the switch and arranged to preset the mode in response to operationof the switch, an indicator for indicating the mode in response to anoutput from the controller, the controller being arranged to output aplurality of indications of different modes in a sequence, and to selectthe mode just indicated upon an operation of the switch.

Preferably, the switch is mounted inside the probe but is operable by anactuator accessible from outside the probe.

In a first embodiment the switch comprises a push button.

In a second embodiment of the invention the probe has aworkpiece-contacting stylus mounted on a seat from which it isdeflectable, wherein the stylus and the seat comprise said switch. Theseat may be kinematic. The controller receives an input from the switchwhen the stylus is deflected.

Each mode may also include a plurality of different sub-modes. Thecontroller may be arranged to output a plurality of indications ofdifferent sub-modes in a sequence and select the sub-mode just indicatedupon an operation of the switch.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described withreference to the accompanying drawings, wherein:

FIG. 1 is a diagrammatic view of a probe on a machine tool;

FIG. 2 is a partly sectional view of part of a first embodiment of theprobe of FIG. 1;

FIG. 3 is a block circuit diagram showing a micro controller within theprobe;

FIG. 4 is a flow chart of a program of the first embodiment which runsin the micro controller;

FIG. 5 is a side view of the second embodiment of the probe;

FIG. 6 is a sectional view of the probe of FIG. 5 through A-A;

FIG. 7 is a sectional view of the probe of FIG. 5 through B-B; and

FIG. 8 is a flow chart of a program of the second embodiment which runsin the micro-controller.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring to FIG. 1, a probe 10 is mounted in the spindle 12 of amachine tool, exchangeably with the normal cutting tools. The spindle 12can move the probe in three dimensions X,Y,Z, relative to a workpiece 14clamped on the table or bed 22 of the machine tool. Measurements aremade by contact between a stylus 11 of the probe and the workpiece.Measurement signals from the probe are transmitted optically, asindicated by arrow 16, to a receiver module 19 mounted on fixedstructure 20 of the machine tool. The module 19 can also transmit anoptical (e.g. infrared) switch-on or start signal, indicated by arrow18, to the probe 10. The probe 10 is battery operated, and remains in asleeping state until receipt of the switch-on signal 18, whereupon itstarts transmitting measurement signals 16.

FIG. 2 shows a first embodiment of the probe 10 in more detail.Internally, it has two circuit boards 24, on which are fitted lightemitting diodes 26 for transmitting the optical measurement signals 16.The boards 24 also have a plurality of photodiodes 28 (only one of whichcan be seen in FIG. 2), for receiving the switch-on signal 18.Furthermore, they have indicators in the form of red and green lightemitting diodes (LEDs) 44,45. The light emitting diodes 26, thephotodiodes 28 and the indicator LEDs 44,45 are distributed around thecircumference of the probe, behind a glass window 30.

One of the circuit boards 24 is provided with a push button switch 32.This can be operated from externally of the probe, by means of anactuator 34 in the form of a plunger. The external end 36 of thisplunger lies within a recess 38, and can be actuated by means of asuitable pointed implement.

The following table illustrates various possible modes which can bepreset by the use of the push button switch 32. TURN OFF SELECT FILTERSELECT MODE OPTICAL TIME 10 sec TIME 30 sec TIME 134 sec NO FILTERANALOGUE DIGITAL 1 √ √ 2 √ √ 3 √ √ 4 √ √ 5 √ √ 6 √ √ 7 √ √ 8 √ √ 9 √ √10 √ √ 11 √ √ 12 √ √

It will be seen that the items which can be selected fall into twogroups. Under the heading “turn off select” there are variouspresettable possibilities for the manner in which probe circuitry isturned off (i.e. returned to its sleeping state in which it no longertransmits measurement signals 16). The first column under this headingindicates modes in which the probe circuitry is turned off by thereceipt of another optical signal from the machine-mounted module 19, asindicated by the arrow 18. The remaining columns under this headingindicate that the probe is turned off after a preset period of non-use(i.e. during which the stylus 11 of the probe 10 has not contacted theworkpiece 14). In various different modes, the probe may be turned offafter periods of 10 seconds, 30 seconds or 134 seconds of non-use.

The final three columns of the above table, labelled “filter select”,indicate possible filtering which may be applied to the probemeasurement signal before it is transmitted as the optical signal 16.The filtering selected will depend upon the machine to which the probeis installed and the environment. If the installation is not susceptibleto vibration, then modes in which no filtering is performed may bepreset. Alternatively, in different installations, modes with analoguefiltering or digital filtering may be preset.

It will be seen that the table shows 12 possible modes, which betweenthem give all possible combinations of “turn off select” and “filterselect”.

The push button 32 provides an input to a micro controller 40, seen inFIG. 3. This has outputs 42 to the remaining circuitry on the circuitboards 24, which provide the various possibilities for turn off andfiltering indicated in the above table. It also controls the lightemitting diode indicators 44.

Referring to FIG. 4, the micro controller 40 acts as follows. In step46, in the sleeping state, the micro controller's program detects thatthe button 32 has been pushed. In steps 47,48 and 49, it determineswhether the button remains pushed for a period greater than 3 seconds.If the button is released within this 3 second period, then in programstep 50 the micro controller outputs signals to the indicator 44 toindicate the current mode which has been preset previously. It does thisby flashing the indicator 44 a number of times, corresponding to themode number indicated in the above table (e.g. 3 flashes for mode 3).

Thus, the operator can obtain an indication of the current mode simplyby depressing the button briefly (for less than 3 seconds). If desired,an alternative period such as 5 seconds may be used.

If the button is held depressed for more than 3 seconds, the programenters a loop comprising steps 51 to 59. Firstly, step 51 sets the modenumber to 1, and step 52 provides an output to the indicator 44 toindicate this mode. Alternatively, step 51 may be omitted and the loopcan start with the mode currently set. As in step 50, the mode isindicated by a corresponding number of flashes of the indicator 44.

Next, in steps 53,54 and 56, the program pauses, for example for 2seconds, while checking the state of the button. If the button isreleased during this pause, (step 54) the program exits the loop, and instep 60 the micro controller provides outputs on the lines 42 to presetthe filters and the turn off circuits of the probe. It does so inaccordance with the mode last set in step 51.

If, in step 56, the button has not been released at the end of the 2second pause, then the loop continues, via program step 58 whichincrements the mode number. Should the maximum number of modes have beenexceeded, then step 59 returns to the loop via step 51, which resets themode number to 1. The new mode is now indicated in step 52, and steps53,54 and 56 pause to see if the operator releases the button.

Mode selection is therefore a very easy process for the operator. Hesimply presses the button, and holds it depressed while the programcycles through all the possible modes. He releases the buttonimmediately after the mode required has been indicated. Thus, if herequires mode 5, he releases the button after the part of the cycle inwhich the indicator 44 flashes five times.

Of course, modifications are possible. In the above description, eachtime the program passes through step 52 it flashes for a number of timescorresponding to the mode number (once for mode 1, five times for mode5, etc). It may instead simply flash once on each pass through thisprogram step. The operator then effectively counts the number of timesthat the program passes around the loop 52,53,54,56,58, releasing thebutton 32 at the appropriate time.

It is also possible to provide a more sophisticated indicator 44, givinga numerical indication, instead of a number of flashes.

It will also be appreciated that the modes indicated in the table aboveare intended merely as examples. Other aspects of the operation of theprobe may be preset in the various modes, in addition or instead of thefiltering and the turn off method.

The push button 32 in this preferred embodiment overcomes the problemsof DIP switches discussed in the introduction.

A second embodiment of the probe 10 is shown in FIGS. 5-7. FIGS. 6 and 7are sections along the lines A-A and B-B respectively shown in FIG. 5.The probe 10 comprises a housing 24 and a stylus 11.

The electronics are mounted on a flexible material 70 which ispositioned in a compact spiral arrangement along the insidecircumference of the probe housing. The electronics include lightemitting diodes 26 for transmitting the optical measurement signals 16,a plurality of photodiodes 28 for receiving the switch-on signal 18 andindicators 44 in the form of red and green light emitting diodes forindicating the mode. The light emitting diodes 26, photodiodes 28 andindicators 44 are distributed around the circumference of the probebehind a glass window 30.

The stylus 11 is mounted on a kinematic seat inside the housing. Thekinematic seat comprises three vee-shaped grooves each formed between apair of ball bearings 72. The stylus has three cylindrical members 74extending radially from its upper end which are urged into contact withthe vee-shaped grooves by a spring 76. This defines the rest position ofthe stylus 11. Such an arrangement is well known and described in U.S.Pat. No. 4,153,998.

When the stylus is in this rest position an electric circuit whichpasses in series from one vee-shaped groove to the next adjacent one iscompleted. Each member is insulated from the stylus and other membersand completes the circuit between the two sides of each respectivevee-shaped groove. Deflection of the stylus results in at least one ofthe members breaking contact with the ball bearings and thus breakingthe circuit. As described in U.S. Pat. No. 4,153,998 the breaking of thecircuit is used to provide an input pulse to an automatic switchingarrangement and thereby indicate that deflection of the stylus hasoccurred. In the present invention, this arrangement may also be used asa switch for changing between different preset modes, for example forselecting turn-off modes or selecting different filters.

The following table illustrates various possible modes which can bepreset by using the probe stylus. MODE OPTION Turn-off mode selectOptical off Short timeout Medium timeout Long timeout Probe filterselect Probe filter on Probe filter off Start filter select StartRejection filter on Start Rejection filter off

In this example there are three modes each mode having several options.The first mode in the table selects the turn-off method and has fouroptions for pre-setting the manner in which the probe circuitry isturned off, as described in the previous embodiment. In the first optionthe probe circuitry is turned off following an optical signal from themachine mounted module as indicated by arrow 18 in FIG. 1. The remainingoptions indicate that the probe is turned off after a preset period ofnon-use, i.e. during which the probe stylus has not contacted theworkpiece. For example, for a short time-out the probe turns off afterabout 10 seconds of non-use. A medium time-out may be about 30 seconds,and a long time-out may be about 134 seconds of non-use.

The second mode in the table is probe filter select as described in theprevious embodiment. In this mode the options are the probe filter maybe on or off.

The third mode in the table is the start signal filter select. Thisfilter enables the probe to distinguish between the start signal (18 inFIG. 1) and other external influences, such as light from fluorescentlight bulbs, which may be confused with the start signal. However thisfilter introduces a time delay and thus may not be required whenexternal influences are insignificant. In this mode, the options are thestart signal filter may be on or off. Such a filter is disclosed in ourEuropean Patent Application No. 1130557.

As shown in FIG. 3 the stylus is used as a switch 32 to provide an inputto a micro-controller 40. This micro-controller sends outputs 42 to thecircuitry in the probe which allows different modes to be selected anddifferent options within each mode to be selected. The micro-controlleralso controls the light emitting diode indicators 44 which flashdifferent signals to indicate the different modes and options.

Referring to FIG. 8, the micro-controller 40 acts as follows. Themicro-controller is in a sleep mode 88 until it detects a battery beinginserted 80 in the probe which starts a first timer 82. If the kinematicremains seated 84 (i.e. the stylus remains undeflected) for longer than8 seconds 86, the probe will return to the sleep mode 88. However if thekinematic is unseated 84 for longer than 8 seconds 90, then once thekinematic has reseated 92 the mode and option will both be set to thefirst mode and option respectively 94 and the micro-controller willenter the mode and option setting loop 96-114. Alternatively this stepcan be omitted and the loop can start with the mode and option currentlyset.

Thus the micro-controller is activated by inserting the battery and themode and option setting loop of the controller is entered by deflectingthe stylus for a time period of eight seconds and then returning thestylus to its rest position.

When the mode and option setting loop 96-114 is entered a second timeris started 96 and the mode and option are displayed 98 by the indicator.As in the previous embodiment the indicator comprises LEDs. If more than10 seconds has elapsed 100 without the kinematic unseating, then themicro-controller will return to its sleep mode 88.

If the kinematic unseats 102 within 10 seconds 100 then a third timer isstarted 104. If the kinematic reseats within 0.3 seconds 108, themicro-controller will return to the beginning of the loop at 96. If thekinematic has been unseated for greater than 0.3 seconds but less than 2seconds 110 then the option is advanced 112. If the kinematic has beenunseated for greater than 2 seconds then the mode is advanced.

Thus once the micro-controller is in the mode and option setting loop,the option and mode may be advanced by deflecting the stylus for a shorttime period (i.e. for advancing the option) or a longer time period(i.e. for advancing the option).

Once either the mode or option are advanced, the micro-controllerreturns to the beginning of the loop 96-114. The second timer is started96 and the new mode and option are displayed 98. The loop is exited ifthe kinematic remains seated for 10 seconds 100. Otherwise themicro-controller continues around the loop until the desired mode andoption have been selected.

The function of the first, second and third timers 82,96,104 may all becarried out by a single timer.

Use of the stylus on its kinematic mount as a switch has severaladvantages. This arrangement is compact and so the size of the probe isable to be reduced. In addition, the kinematics for the stylus are partof the existing probe and thus no additional parts are needed.

In the above description the indicator flashes a number of timescorresponding to the mode number and option number each time it cyclesthrough the different modes and options. It is also possible to providea more sophisticated indicator giving a numerical indication instead ofa number of flashes.

The above example has three modes, each mode having several options.Therefore the micro-controller can cycle between the three modes untilthe desired mode is selected and then cycle between the options of thatmode until the desired option is selected. This is much quicker thancycling through every option of every mode in turn. The modes andoptions in the table are intended merely as examples. Other aspects ofthe operation of the probe may be preset in the various modes inaddition or instead of the filtering and turn-off method.

1. A measurement probe for position determining apparatus, themeasurement probe comprising: a surface sensor; internal circuitrycapable of operating in a plurality of different modes; a switch; and acontroller connected to receive an input from the switch and arranged toset a mode in response to operation of the switch.
 2. The measurementprobe according to claim 1 wherein the measurement probe includes anindicator for indicating the mode in response to an output from thecontroller.
 3. The measurement probe according to claim 1 wherein thecontroller is arranged to output a plurality of indications of differentmodes in a sequence.
 4. The measurement probe according to claim 1wherein the switch is mounted inside the probe and operated by anactuator accessible from outside the probe.
 5. The measurement probeaccording to claim 1 wherein the switch comprises a push button switch.6. The measurement probe according to claim 1 wherein the surface sensorcomprises a surface contacting stylus.
 7. The measurement probeaccording to claim 6 wherein the stylus is deflectable.
 8. Themeasurement probe according to claim 7 wherein the switch comprises thestylus.
 9. The measurement probe according to claim 8 in which thestylus is mounted on a seat from which it is deflectable, wherein thestylus and the seat comprise said switch.
 10. The measurement probeaccording to claim 8 wherein the controller receives an input from theswitch when the stylus is deflected.
 11. The measurement probe accordingto claim 2 wherein the indicator comprises at least one light emittingdiode.
 12. The measurement probe according to claim 2 wherein anindication of the current mode may be obtained by operating the switchfor less than a certain time period.
 13. The measurement probe accordingto claim 1 wherein if the switch is operated for greater than a certaintime period, the controller enters a mode setting loop.
 14. Themeasurement probe according to claim 1 wherein each mode may alsoinclude a plurality of different sub-modes.
 15. The measurement probeaccording claim 1 wherein the controller is activated by inserting abattery into the probe.
 16. A measurement probe for position determiningapparatus; the measurement probe comprising: a surface contactingstylus; internal circuitry capable of operating in a plurality ofdifferent modes; a switch; and a controller connected to receive aninput from the switch and arranged to set a mode in response tooperation of the switch.
 17. The measurement probe according to claim 16wherein the surface contacting stylus is deflectable.
 18. A measurementprobe for position determining apparatus, the measurement probecomprising: internal circuitry capable of operating in a plurality ofdifferent modes; a switch; and a controller connected to receive aninput from the switch and arranged to set a mode in response tooperation of the switch.